Cell Surface Remodeling of Mycobacterium abscessus under Cystic Fibrosis Airway Growth Conditions.

Understanding the physiological processes underlying the ability of Mycobacterium abscessus to become a chronic pathogen of the cystic fibrosis (CF) lung is important to the development of prophylactic and therapeutic strategies to better control and treat pulmonary infections caused by these bacteria. Gene expression profiling of a diversity of M. abscessus complex isolates points to amino acids being significant sources of carbon and energy for M. abscessus in both CF sputum and synthetic CF medium and to the bacterium undergoing an important metabolic reprogramming in order to adapt to this particular nutritional environment. Cell envelope analyses conducted on the same representative isolates further revealed unexpected structural alterations in major cell surface glycolipids known as the glycopeptidolipids (GPLs). Besides showing an increase in triglycosylated forms of these lipids, CF sputum- and synthetic CF medium-grown isolates presented as yet unknown forms of GPLs representing as much as 10% to 20% of the total GPL content of the cells, in which the classical amino alcohol located at the carboxy terminal of the peptide, alaninol, is replaced with the branched-chain amino alcohol leucinol. Importantly, both these lipid changes were exacerbated by the presence of mucin in the culture medium. Collectively, our results reveal potential new drug targets against M. abscessus in the CF airway and point to mucin as an important host signal modulating the cell surface composition of this pathogen

Acylation of glycerolipids in mycobacteria

We report on the existence of two phosphatidic acid biosynthetic pathways in mycobacteria, a classical one wherein the acylation of the sn-1 position of glycerol-3-phosphate (G3P) precedes that of sn-2 and another wherein acylations proceed in the reverse order. Two unique acyltransferases, PlsM and PlsB2, participate in both pathways and hold the key to the unusual positional distribution of acyl chains typifying mycobacterial glycerolipids wherein unsaturated substituents principally esterify position sn-1 and palmitoyl principally occupies position sn-2. While PlsM selectively transfers a palmitoyl chain to the sn-2 position of G3P and sn-1-lysophosphatidic acid (LPA), PlsB2 preferentially transfers a stearoyl or oleoyl chain to the sn-1 position of G3P and an oleyl chain to sn-2-LPA. PlsM is the first example of an sn-2 G3P acyltransferase outside the plant kingdom and PlsB2 the first example of a 2-acyl-G3P acyltransferase. Both enzymes are unique in their ability to catalyze acyl transfer to both G3P and LPA.This work was supported by the National Institute of Allergy and Infectious Diseases (NIAID)/National Institutes of Health (NIH) grants AI064798 and AI155674 (to M.J.) and by the Spanish Ministry of Science and Innovation grants BFU2016-77427-C2-2-R, PID2019-105649RB-I00 and PID2022-138694OB-I00 (to M.E.G.).Peer reviewe

Cloning and Partial Characterization of an Endo-α-(1→6)-d-Mannanase Gene from Bacillus circulans

Mycobacteria produce two major lipoglycans, lipomannan (LM) and lipoarabinomannan (LAM), whose broad array of biological activities are tightly related to the fine details of their structure. However, the heterogeneity of these molecules in terms of internal and terminal covalent modifications and complex internal branching patterns represent significant obstacles to their structural characterization. Previously, an endo-α-(1→6)-D-mannanase from Bacillus circulans proved useful in cleaving the mannan backbone of LM and LAM, allowing the reducing end of these molecules to be identified as Manp-(1→6) [Manp-(1→2)]-Ino. Although first reported 45 years ago, no easily accessible form of this enzyme was available to the research community, a fact that may in part be explained by a lack of knowledge of its complete gene sequence. Here, we report on the successful cloning of the complete endo-α-(1→6)-D-mannanase gene from Bacillus circulans TN-31, herein referred to as emn. We further report on the successful production and purification of the glycosyl hydrolase domain of this enzyme and its use to gain further insight into its substrate specificity using synthetic mannoside acceptors as well as LM and phosphatidyl-myo-inositol mannoside precursors purified from mycobacteria

Mycobacterial arabinan biosynthesis: characterization of AftB and AftC arabinosyltransferase activity using synthetic substrates

2011 Fall.Includes bibliographical references.Tuberculosis (TB) is a chronic infectious disease caused by M. tuberculosis (Mtb). Treatment of TB is prolonged, and multidrug resistant (MDR-TB) and extensively drug resistant TB (XDR-TB) cases are ever increasing. Efforts to discover and develop new drugs have increased in recent years so improvement of the existing therapies is urgently needed. The cell wall of Mtb with its unique physiological properties has historically been an important and valid drug target. Mycobacterial arabinosyltransferases are membrane bound glycosyltransferases involved in the biosynthesis of the arabinan portion of two major polysaccharides, arabinogalactan (AG) and lipoarabinomannan (LAM), associated with the cell wall. In this work, M. smegmatis was used as a model organism to study arabinosyltransferases and the biosynthesis of cell wall arabinofuran—the main constituent of AG and LAM. This dissertation addresses the development of a cell free arabinosyltransferase assay for AftB and AftC glycosyltransferases. Since it was not possible to express AftB transmembrane protein, we probed AftB transferase activity from the crude membranes using a synthetic arabinose disaccharide acceptor. In this study, a robust cell free iii radioactive arabinosyltransferase assay was developed using a linkage specific synthetic disaccharide acceptor. Relative mobility of the enzymatic product on a thin layer chromatogram and autoradiography clearly demonstrated the enzymatic conversion of the disaccharide acceptor to a trisaccharide. The trisaccharide product was further confirmed by matrix assisted laser desorption ionization- time of flight (MALDI-TOF) or high pH anion exchange chromatography (HPAEC) analysis. GC-MS analysis showed that the additional arabinose added to the enzymatic product was (1→2) linked. This assay is dependent on time and enzyme concentration and the product formation is not sensitive to the action of ethambutol or the absence of the putative arabinosyltransferases encoded by embA, embB or embC. Additionally, further optimal conditions were determined including buffers, pH, divalent cations, detergents, and the effect of alkylating and reducing agents. In a contiguous study, we wanted to convert this assay into a non-radioactive assay for the screening of compounds. We successfully developed an ELISA based non-radiolabeled arabinosyltransferase assay using CS35-mAb that recognized (1→2) linked enzymatic product. As this method involves several washing steps and time consuming processes, we further modified the substrate with fluorescent labeling, however, we failed to establish a fluorescence based arabinosyltransferase assay. Unlike AftB, in a parallel study we were successful in expressing, solubilizing and purifying Mtb AftC. We developed an in vitro transferase assay using purified recombinant AftC and demonstrated that AftC retains transferase activity only when reconstituted into proteoliposomes. Additionally, we were successful in synthesizing alternate arabinose donors Z-nerylphosphoryl D-arabinose (Z-NPA), Z,Z-farnesylphosphoryl D-arabinose (Z-FPA), E,E-farnesylphosphoryl D-arabinose (E-FPA), and Z,Z,Z,Z,E,E-heptaprenylphosphoryl D-arabinose (Z-HPA). Among these lipid donors, Z-FPA demonstrated better solubility in the assay buffer compared to the native donor decaprenyphophoryl D-arabinose (DPA). This dissertation describes screening of drug candidate compounds using a microtiter plate based whole cell Alamar Blue assay. We have successfully screened nearly three thousand compounds for Mtb growth inhibition

Biosynthesis of the Methylthioxylose Capping Motif of Lipoarabinomannan in Mycobacterium tuberculosis

International audienc

Identification of a Novel Mycobacterial Arabinosyltransferase Activity Which Adds an Arabinosyl Residue to α‑d‑Mannosyl Residues

The arabinosyltransferases responsible for the biosynthesis of the arabinan domains of two abundant heteropolysaccharides of the cell envelope of all mycobacterial species, lipoarabinomannan and arabinogalactan, are validated drug targets. Using a cell envelope preparation from <i>Mycobacterium smegmatis</i> as the enzyme source and di- and trimannoside synthetic acceptors, we uncovered a previously undetected arabinosyltransferase activity. Thin layer chromatography, GC/MS, and LC/MS/MS analyses of the major enzymatic product are consistent with the transfer of an arabinose residue to the 6 position of the terminal mannosyl residue at the nonreducing end of the acceptors. The newly identified enzymatic activity is resistant to ethambutol and could correspond to the priming arabinosyl transfer reaction that occurs during lipoarabinomannan biosynthesis

A Small Multidrug Resistance-like Transporter Involved in the Arabinosylation of Arabinogalactan and Lipoarabinomannan in Mycobacteria*

International audienceBackground: (Glyco)lipid translocation across the plasma membrane plays a pivotal role in the biogenesis of the mycobacterial cell envelope. Results: The SMR-likes transporter Rv3789 appears to be involved in reorienting decaprenol phosphate arabinose to the periplasm. Conclusion: Rv3789 participates in the buildup of the arabinan domains of arabinogalactan and lipoarabinomannan. Significance: This is the first lipid-linked sugar translocase ever identified in mycobacteria

Biosynthesis of the Methylthioxylose Capping Motif of Lipoarabinomannan in <i>Mycobacterium tuberculosis</i>

Lipoarabinomannan (LAM) is a lipoglycan found in abundant quantities in the cell envelope of all mycobacteria. The nonreducing arabinan termini of LAM display species-specific structural microheterogeneity that impacts the biological activity of the entire molecule. <i>Mycobacterium tuberculosis</i>, for instance, produces mannoside caps made of one to three α-(1 → 2)-Man<i>p</i>-linked residues that may be further substituted with an α-(1 → 4)-linked methylthio-d-xylose (MTX) residue. While the biological functions and catalytic steps leading to the formation of the mannoside caps of <i>M. tuberculosis</i> LAM have been well established, the biosynthetic origin and biological relevance of the MTX motif remain elusive. We here report on the discovery of a five-gene cluster dedicated to the biosynthesis of the MTX capping motif of <i>M. tuberculosis</i> LAM, and on the functional characterization of two glycosyltransferases, MtxS and MtxT, responsible, respectively, for the production of decaprenyl-phospho-MTX (DP-MTX) and the transfer of MTX from DP-MTX to the mannoside caps of LAM. Collectively, our NMR spectroscopic and mass spectrometric analyses of <i>mtxS</i> and <i>mtxT</i> overexpressors and knockout mutants support a biosynthetic model wherein the conversion of 5′-methylthioadenosine, which is a ubiquitous byproduct of spermidine biosynthesis, into 5′-methylthioribose-1-phosphate precedes the formation of a 5′-methylthioribose nucleotide sugar, followed by the epimerization at C-3 of the ribose residue, and the transfer of MTX from the nucleotide sugar to decaprenyl-phosphate yielding the substrate for transfer onto LAM. The conservation of the MTX biosynthetic genes in a number of Actinomycetes suggests that this discrete glycosyl substituent may be more widespread in prokaryotes than originally thought